Crosschecking the schematics mentioned earlier in this topic with my soon to be installed seats, and pictures of actual wirings and descriptions of the functionality by others, my thought was that something was wrong with the schematic. Long story short, the schematic mentioned in this thread is for phase 1 only. Phase 2 and up the power is no longer constantly connected to the seats, but is switched using relais turning the ignition key. Basically when you turn your ignition key once, the seats are powered, and when you turn on the lights, the background lighting in the heating switch is turned on. Heating can be used when turning the ignition as well.
There is also an override for the ignition key switch relais from the courtesy lighting system, using a 2nd relais. (white/purple wire, coming from the ISCU) This means that after you remove the key, or when you step into the car and you did not yet entered the key, you have 3 minutes in which you can still use the electric adjustments of the seats. It's the same system that makes the interior lighting go out automatically.
The schematics can be found in the manual. Mind you, there is a fault in the schematic, the ground of the electric adjustment part is connected to the power that lights the heating switch
Italian engineering i guess... make sure you just connect all grounds to the main one.
Sadly enough for me, the actual wiring loom did not come with my seats, so i have to build my own. No big deal, but i am not going to replicate the courtesy lighting part.